1. Filed of the Invention
The present invention relates to an electroless plating pre-treatment solution used in pre-treatment of electroless plating and an electroless plating method using this electroless plating pre-treatment solution.
2. Description of the Related Art
In order to achieve higher integration density and higher function of a semiconductor device, there has arisen a demand for the improvement in the operation speed of the device in recent years. In accordance with this demand, wiring for element connection has become finer and multileveled. In order to respond to the finer wiring structure and more multilevel interconnection, Cu is currently used as a wiring material and a damascene method is adopted. This method is a method of forming the wiring by forming a wiring film on the surface of an interlayer insulation film having wiring grooves, and thereafter removing the wiring film, leaving only portions thereof in the wiring grooves.
In order to realize the finer wiring structure, research and technical development are underway to realize a lower dielectric constant interlayer insulation film and improve electromigration (EM) resistance of Cu. As a technique of improving the EM resistance, a cap metal technique is known. This technique is to selectively form, on Cu wiring, different metal by an electroless plating method to improve adhesiveness of the interface. Incidentally, when a cap metal film is imparted a diffusion preventive property to Cu, an etch stopper film can also have a lower dielectric constant, so that it is possible to lower an effective dielectric constant.
Electroless plating currently adopted for forming a cap metal film uses dimethylamine borane (DMAB), hydrophosphite, or the like as a reducing agent (see, for example, Japanese Patent Application Laid-open No. 2002-151518). Here, if dymethylamine borane is used as the reducing agent, it is possible to apply plating on the Cu wiring without any help by a precious metal catalyst such as Pd since Cu has catalytic activity to an oxidative decomposition reaction of dimethylamine borane. On the other hand, if hydrophosphite is used as the reducing agent, a precious metal catalyst such as Pd is added in applying plating on the Cu wiring since Cu does not have catalytic activity to hydrophosphite.
However, the surface of the Cu wiring becomes inactive due to the adhesion of an antioxidant or the like and surface oxidation that are caused by chemical mechanical polishing (CMP) and a cleaning process. Therefore, cleaning and activating processes are required. Especially in the use of dimethylamine borane as the reducing agent, the time from the start of the supply of an electroless plating solution to the start of a plating reaction (hereinafter, referred to as “incubation time”) is long and unstable, so that forming the cap metal film on the Cu wiring requires difficult time management and is time-consuming. Further, in the use of hydrophosphite as the reducing agent, precious metal with a strong catalytic force such as Pd is used for surface substitution, which results in cost increase, though shortening the incubation time.